Downhill snow skiing (also known as alpine skiing) is a popular cold-weather outdoor sport requiring skill and proper equipment. Standard skiing equipment includes the skis themselves, ski boots, ski bindings, and ski poles. The ski bindings are mounted to the skis and are designed to hold the boot to the ski at most times, but to release the boot if it pulls away from the ski in such a way that an injury to the skier might occur. Conventional ski bindings contain spring-loaded jaws which are adjusted for tension according to the skiing conditions and the weight and skill of the skier. Conventional ski bindings are purely mechanical ana base their retention/release decision solely on the forces which develop between the boot and the binding.
The role of ski bindings in reducing the risk of injury during skiing has long been recognized. Within the past decade, it has also been found that the ski boot itself can play a major role in injury reduction. Older ski boots were relatively rigid and permitted little movement of the lower leg relative to the foot. As a result, many breaks of the tibia (the lower leg bone) occurred at a location corresponding to the top of the boot. Modern ski boots permit much more flex, especially forward flex. Many ski boots now contain separate leg and foot sections which are connected together with ankle pivots. The combination of modern ski bindings and improved ski boots has led to an 88 percent reduction in tibia fractures over a recent 15 year period. R. J. Johnson et al., "Skier Injury Trends," Seventh International Symposium on Skiing Trauma and Safety, American Society for Testing and Materials, Philadelphia, Pa. 1989.
Unfortunately, while tibia fractures and ankle sprains have been decreasing, serious knee injuries have shown a 2.7-fold increase. Knee injuries currently account for more than 20 percent of all alpine skiing injuries and the knee has become the most common injury site. It has been suggested that two major factors are responsible for the persistence of the knee injury rate: (1) Conventional ski bindings do not offer sufficient modes of release to protect the knee; and (2) The knee can become the weak link in the lower extremity because its strength varies as a function of the angle of knee flex. S. M. Maxwell et al., "Measurement of Strength and Loading Variables on the Knee During Alpine Skiing," Seventh International Symposium on Skiing Trauma and Safety, American Society for Testing and Materials, Philadelphia, Pa. 1989. More specifically, it is known that the knee is weakest when hyperflexed or fully extended and is strongest when bent slightly. When the knee is weakest, it is susceptible to serious injuries such as sprains or tears of the anterior cruciate ligament. Accordingly, S. M. Maxwell et al. suggest the desirability of a ski binding that incorporates some method of determining knee strength to satisfy release and retention requirements simultaneously.
Although there is no commercial ski binding available which bases its retention/release decision on knee strength, a number of ski bindings have been disclosed which employ electronics in the retention/release decision. For example, Smolka, U.S. Pat. No. 3,776,566, issued Dec. 4, 1973, discloses a ski binding containing sensors mounted onto the foot which pick up bio-electrical currents from muscle movements. When the currents reach a preselected value, the binding is automatically released. Courvoisier et al., U.S. Pat. No. 3,909,028, issued Sep. 30, 1975, discloses a ski binding having a sensor which detects twisting of the lower leg. Sittmann, U.S. Pat. No. 3,947,051, issued Mar. 30, 1976, discloses a ski binding having sensors on the foot which detect forces between the foot and the boot and cause the binding to release when these forces become excessive.
Accordingly, a need still exists for a ski binding which reduces the risk of knee injuries by basing its retention/release decision, at least in part, on knee strength.